Treatment with botulinum toxin injections does not change brainstem interneuronal excitability in patients with cervical dystonia.

Brainstem interneuronal excitability is enhanced in patients with cervical dystonia. Treatment with local botulinum toxin (BTX) injections temporarily alleviates the pain and weakens the muscle spasms, characteristics of this condition. In 10 patients with cervical dystonia, we studied whether the clinical improvement induced by BTX was associated with modification of the blink reflex excitability recovery curve to paired supraorbital nerve electrical shocks. We found that the mean percentage recovery of the R2 to the test stimulus was abnormally enhanced before treatment and that it did not significantly change after treatment, at the time of maximal clinical improvement, in any of the interstimulus intervals tested. We conclude that the clinical improvement induced by BTX in patients with cervical dystonia is largely symptomatic and is not related to any change of the known abnormalities in brainstem interneuronal excitability that possibly underlie the pathophysiology of cervical dystonia.